1. Field of the Invention
The present invention relates generally to data communications, and more specifically to a cellular mobile communication system where mobile data terminals send and receive packets to and from cell-site stations.
2. Description of the Related Art
Recent proliferation of personal devices for cellular mobile communication networks have created a need to communicate computer data over radio links in a packet-switched mode, rather than in a circuit-switched mode, for efficient utilization of network resources. In data communication systems, the international standard X.25 specifies that three-bit serial numbers be contained in each data packet to indicate the transmit and receive sequences together with a format identifier and a logical channel number and so fort. According to the X.25 standard, a predetermined number of data packets are transmitted in sequence from a transmit site to a receive site. These packets are called "outstanding" because the transmit site receives no acknowledgment during the transmission of these packets. If the receive site ails to receive any of the outstanding packets it returns no acknowledgment. Following the transmission of all outstanding packets, the transmit site begins a timing operation. If no acknowledgment is received within the period of the timing operation, the transmit site determines that an error has occurred in the transmitted packets, and retransmits their copies although not all of the previous packets have been corrupted.
If the protocols of the current standard for packet switched network are employed, the throughput of a connection established in the cellular network will be significantly low due to the relatively low transmission speed of the radio link. Another factor that would affect the throughput is the amount of data contained in the packet header since powerful error control bits would be needed to ensure against the loss of any single bit. Furthermore, the conventional retransmission scheme would increase radio traffic and hence place further limitations on the throughput. It is thus important to reduce the amount of housekeeping data in the packet header.